The invention is directed to a method for stabilizing glide shoes loaded against an inner face of a rotating mantle of a roll having adjustable pressure zones, in which the glide shoes are supported by means of an articulated joint or equivalent on pistons or equivalent which load the glide shoes with adjustable pressure.
The present invention is also directed to a hydrostatic or substantially hydrodynamic glide shoe intended for carrying out the method of the present invention in which the glide shoe comprises one or several lubrication chambers, into which pressurized lubricant is passed by means of which the glide face of the glide shoe is lubricated.
The present invention is additionally directed to a roll for a paper machine having adjustable pressure zones, for the above method of the present invention, and/or utilizing the above glide shoes in accordance with the present invention, such as a press roll or a calender roll. This paper machine roll comprises a revolving mantle and a stationary axle fitted inside the mantle, with a number of cylindrical bores or equivalent in the axle which can be loaded by means of a pressurized medium, and in which pistons or equivalent are situated. The pistons or equivalent substantially centrally load the glide shoes against an inner face of the revolving cylindrical mantle, through articulated joints or equivalent.
In paper machines, several such rolls are used to form, e.g. a dewatering press nip, a smoothing nip, or a calendering nip with a counter-roll. In these purposes of use, it is important that the distribution of the linear load, i.e. the pressure profile of a nip over the axial direction of the rolls, must be made constant, or that this profile can be adjusted as desired, e.g., so as to control the transverse moisture profile and/or thickness profile of the web. For this purpose, various adjustable-crown or variable-crown rolls have been known in the prior art, with attempts having been made to act upon the distribution of the linear load in a nip by means of these rolls.
In the prior art, several different variable-crown rolls or adjustable-crown rolls for paper machines have been known. As a rule, these rolls each comprise a massive, stationary roll axle and a roll mantle arranged to revolve about the axle. Between the axle and the mantle, acting upon an inner face of the mantle, glide-shoe arrangements and/or pressure-fluid chambers have been fitted, such chambers being divided into several parts over the axle direction of the roll, so that the axial profile of the mantle at the nip can be aligned or adjusted as desired. As a rule, the nips formed by such rolls, such as press nips or calendering nips, are loaded by means of loading forces applied to the axle journals of the variable-crown roll and of its counter-roll. The present invention relates to such variable-crown or adjustable-crown rolls, comprising a series of glide shoes having glide faces hydrostatically lubricated by means of pressurized oil passed onto the respective glide faces.
Prior-art glide shoes of the rolls adjustable in zones, in particular in glide shoes lubricated by means of hydrostatic pressure chambers, have involved the drawback that, especially when oil film is thin, frictional force on the glide face becomes high when the running speed is increased. This frictional force causes a torque that turns the glide face around its support point, which results in making the oil film even thinner at the portion near a front edge of the glide face, with regard to a direction of rotation of the roll mantle, because stabilizing forces in the lubrication chambers are not sufficient to compensate for this torque.
In the prior-art glide shoes, attempts have been made to eliminate the problem discussed above, by shifting the support point of the glide shoe backwardly, or by feeding pressures of different magnitudes into the front and rear chambers (in the direction of rotation). This, however, results in the drawback that the glide shoe becomes asymmetric. The direction of rotation of the roll mantle cannot be reversed for this reason. Such asymmetry also results in difficulties in producing uniformed distribution of pressure on the glide shoe with varying rotational speeds and loads.